This thesis reports studies of methane dehydro-aromatization (MDA) over Zn-based/HZSM-5 catalysts and the catalytic conversion of acetylene gas (C2H2) on grain surface reactions using time-of-flight mass spectrometry (TOF-MS). Both catalytic reactions generate polycyclic aromatic hydrocarbons (PAHs) as their final products. For the MDA reaction, the performance of Zn-based/HZSM-5 catalysts prepared by wet impregnation method was investigated under the conditions of atmospheric pressure and supersonic jet expansion (SJE). The experimental results revealed that, under the SJE condition, the Zn/HZSM-5 catalysts exhibited high catalytic activity. It was also found that because of the rapid migration of H+ ions on the catalyst, the activation of CH4 at active sites of nano-ZnO is facile. A new reaction mechanism involving an active “ZnO-CH3+...-H-ZnO” intermediate formed as a result of synergetic action between ZnO and HZSM-5 has been proposed for the dissociation of methane and dehydrogenation. However, under atmospheric pressure, the catalytic activity of the Zn/HZSM-5 catalysts was low. The physical properties of the catalyst were characterized by Brunauer-Emmett-Teller (BET), Fourier transform infrared (FT-IR), temperature-programmed reduction of H2 (H2-TPR), temperature -programmed desorption of NH3 (NH3-TPD), X-ray photoelectron spectroscopy (XPS), thermogravimetric and differential thermogravimetric (TG/ DTG), and high-resolution transmission electron microscopy (HRTEM) techniques. For the catalytic conversion reaction of acetylene gas to form PAHs, the grains used were olivine and pyroxene-type silicates as well as alumina. Gas-phase PAHs were produced by the catalytic reaction of acetylene over crystalline silicates and alumina in a pulsed jet expansion condition and the gaseous products detected using time-of-flight mass-spectrometry (TOF-MS). In a separate experiment, further confirmation of the catalytic conversion of PAHs was obtained with the acetylene gas at atmospheric pressure flowing continuously through a fixed-bed reactor. The gas effluent and carbonaceous compounds deposited on the catalysts were dissolved separately in dichloromethane and analyzed using gas-chromatography-mass spectrometry (GC-MS). Amongst the samples studied, alumina showed higher activity than the olivine and pyroxene-type silicates grains. A mechanism for PAH formation is proposed in which the Mg2+ in silicates and Al3+ ions in Al2O3 act as Lewis acid sites for the acetylene reactions. Experimental investigation indicated that these silicates and Al2O3 particles are capable of providing catalytic centers for adsorption and activation of acetylene molecules that are present in the circumstellar environments of mass-losing carbon stars. The structure and physical properties of the particles were characterized by means of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and high-resolution transmission electron microscopy (HRTEM) techniques. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

The technique of single-cell analysis using time-resolved inductively coupled plasma-mass spectrometry has been characterized and optimized. Determination of the metal contents of individual cells provides data on the natural metal contents of the cells and the corresponding distributions in the population. The distribution is a useful indicator of the health and the state of development of the cells. The contents of sorbed metals of individual cells over a duration of time are required to understand the dynamics of metal-cell interactions. A green alga, Chlorella vulgaris, was used as a model biological cell in this study. The criteria and procedures for proper sampling of the cells into the ICP will be discussed. Ideally, each ICP-MS spike corresponds to one cell, but cell overlapping occurs because the cells enter the ICP randomly. Selection of cell number density and sample uptake rate to minimize spike overlapping will be discussed. A cell counting method based on the frequency of the spikes has been developed. The distribution of the metal contents of cells was determined by measuring large number of spikes. The minimum number of spikes required was determined by statistical analysis. The spike intensity distribution was correlated with the size distribution of the cells. The peak maximum of the spike intensity distribution was used for the determination of the average metal content of the cells. The use of the peak maximum reduces errors due to spike overlapping in the measurement. Quantitative determination of the metal contents was achieved using standard particles for calibration. Errors in calibration using standard solution nebulization were discussed. The technique was applied in the study of metal-cell interactions. Sorption of heavy metal ions (as environmental pollutants) by Chlorella vulgaris, and uptake of biometal (as nutrient) and metallodrug (as toxin) by Helicobacter pylori were studied. The technique requires simple sample preparation of removing the culture medium by filtration or centrifugation. The health state of the cells in the presence of toxic metals was related to the change in cell number density. The ratio of the FWHM of the spike intensity distributions of the sorbed metals to the natural metal contents of the cells is identified as a possible indicator of the location of the sorbed metals. The kinetics of metal sorption by the cells can be studied using a single cell culture. The method reduces errors due to uncertainties in cell number density and metal concentration in multiple samples that are required in conventional methods. The optimal ICP-MS sampling depth of 17 elements, introduced into the ICP by conventional solution nebulization of aqueous standard solutions, has been determined. The elements were selected to represent a wide range of boiling points and ionization potentials. Boiling point of the dried residues and ionization potential of the analyte element were identified as the major factors that determine the optimal sampling position. Since dried sample solution aerosols are effectively nanoparticles, the study provides useful insight on the optimization of the operation conditions and calibration strategies for single-particle analysis using ICP-MS. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Time-resolved Inductively Coupled Plasma –Mass Spectrometry (ICP-MS) is a versatile tool for the analysis of single particles such as air particles, nanoparticles, and biological cells. In this study, the processes of particle vaporization and analyte atom diffusion and ionization in the ICP were investigated using computer simulation. Gold nanoparticles of particle diameter 10 to 250 nm were used as the model particle. The parameters of the model were optimized with respect to the experimental data. The relative importance of these parameters was investigated. Simulated ICP-MS intensity versus sampling depth for different particle size was calculated. Two models of particle vaporization, namely heat-transfer-limited and mass-transfer-limited, were adopted to describe the kinetics of vaporization of the gold nanoparticles. The rate of particle vaporization of the limiting model in each 5-µs time step was used in the simulation. The heat-transfer-limited process dominates at lower position of the ICP. The mass-transfer-limited process takes over at sampling depth of 4mm or above where the ICP temperature is higher than 4000K. The simulation assumed that the gold atoms vaporized from the particle in each time step diffuse independently. The number density of the gold atoms was calculated using the Chapman-Enskog diffusion theory for each subsequent time step. The degree of ionization of the gold atoms was estimated using Saha equation and was assumed to be dependent on the plasma temperature only. The simulated ICP-MS intensity at any instant was the sum of the gold ions in the ion plumes from all previous time steps that pass through a 1-mm sampler cone. The effects of several simulation parameters on the calculated ICP-MS intensity were investigated. The simulation depth profile of ICP-MS intensity of 100-nm gold nanoparticle was compared to the experimental ICP-MS depth profile. The ICP-MS intensity depends strongly on the ionization temperature of the plasma and the evaporation coefficient of the analyte. The ICP temperature profile, gas velocity, ionization temperature and evaporation coefficient were optimized for the best fit of simulated results to the experimental data. Simulated calibration curves of gold nanoparticles of nominal diameter of 10 nm to 250 nm are non-linear at any sampling depth. The calibration curve rolls off at high mass due to incomplete vaporization of the larger particles in the ICP. The calibration curve at high sampling depth concaves upward in the low mass range because of significant diffusion loss of the analyte atoms for the small particles. / published_or_final_version / Chemistry / Master / Master of Philosophy

abstract / Chemistry / Doctoral / Doctor of Philosophy

abstract / Chemistry / Doctoral / Doctor of Philosophy

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This research focuses on electrothermal vaporization (ETV) as a sample introduction source for inductively coupled plasma mass spectrometry (ICPMS). ETV creates a dry plasma that causes problems when used at the high applied powers (e.g., 1.2 kW) typically employed for nebulizer-based sample introduction for certain ICPMS instruments. A secondary discharge forms in the sampling region of the spectrometer, but this effect was removed by reducing the applied power (e.g., 0.7 kW). A novel, steady state, dry aerosol introduction system was developed to permit optimization of the ICPMS settings. The device used solid NbF₅, SnBr₄ and a W filament plated with Pb to generate dry aerosols which produced ²⁸Si⁺, ⁷⁹Br⁺, ¹²⁰Sn⁺, ¹⁸⁴W⁺, and ²⁰⁸Pb⁺ that were used to optimize the ICPMS. When compared to an ICPMS optimized using a nebulizer, the dry optimized plasma produced an average enhancement of 4.5(±0.4) for 26 elements when using ETV sample introduction. The ETV produces a short (0.5-2 s) transient pulse once every 2-3 min, resulting in a sample throughput of 20-30 samples/h. To increase this throughput, a low power, low background multiplexed ETV device using carbon braids as vaporizers was developed. Oxygen ashing was demonstrated with recoveries of 96±17% for a suite of elements. Refractory elements (e.g., V and U) showed precision of greater than 25% while medium to high volatility elements were in the 10-20% range. The lifetime of the braids was limited to ca. 30 vaporizations when heated to 2,800°C. A device for coupling an ETV in parallel with a nebulizer was also designed and characterized. The device was designed to minimize the impact of the ETV's presence on nebulizer-based ICPMS performance. The ETV could be easily switched on line to provide complimentary information that may be unavailable with nebulizer sample introduction because of isobaric interference problems. For example, in a 1% HCl matrix, the detection limits for ⁵¹V⁺ (⁵¹ClO⁺ interference), ⁷⁵As⁺ (⁷⁵ArO⁺ interference) and ⁷⁸Se⁺ were found to be 0.008 ppb, 0.088 ppb, 0.063 ppb, respectively. By contrast, the nebulizer detection limits in 1% HCl for ⁵¹V⁺, ⁷⁵As and ⁷⁸Se were found to be 0.593 ppb 1.488 ppb and 1.158 ppb, respectively. / text

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The WHO classification of brain tumors is based on histological features and the aggressiveness of the tumor is classified from grade I to IV, where grade IV is the most aggressive. Today, the correlation between prognosis and tumor grade is the most important component in tumor classification. High grade gliomas, glioblastomas, are associated with poor prognosis and a median survival of 14 months including all available treatments. Low grade meningiomas, usually benign grade I tumors, are in most cases cured by surgical resection. However despite their benign appearance grade I meningiomas can, without any histopathological signs, in some cases develop bone invasive growth and become lethal. Thus, it is necessary to improve conventional treatment modalities, develop new treatment strategies and improve the knowledge regarding the basic pathophysiology in the classification and treatment of brain tumors. In this thesis, both proteomics and metabolomics have been applied in the search for biomarkers or biomarker patterns in two different types of brain tumors, gliomas and meningiomas. Proteomic studies were carried out mainly by surface enhanced laser desorption ionization time of flight mass spectrometry (SELDI-TOF-MS). In one of the studies, isobaric tags for relative and absolute quantitation (iTRAQ) labeling in combination with high-performance liquid chromatography (HPLC) was used for protein detection and identification. For metabolomics, gas-chromatography time-of-flight mass spectrometry (GC-TOF-MS) has been the main platform used throughout this work for generation of robust global metabolite profiles in tissue, blood and cell cultures. To deal with the complexity of the generated data, and to be able to extract relevant biomarker patters or latent biomarkers, for interpretation, prediction and prognosis, bioinformatic strategies based on chemometrics were applied throughout the studies of the thesis. In summary, we detected differentiating protein profiles between invasive and non-invasive meningiomas, in both fibrous and meningothelial tumors. Furthermore, in a different study we discovered treatment induce protein pattern changes in a rat glioma model treated with an angiogenesis inhibitor. We identified a cluster of proteins linked to angiogenesis. One of those proteins, HSP90, was found elevated in relation to treatment in tumors, following ELISA validation. An interesting observation in a separate study was that it was possible to detect metabolite pattern changes in the serum metabolome, as an effect of treatment with radiotherapy, and that these pattern changes differed between different patients, highlighting a possibility for monitoring individual treatment response.  In the fourth study of this work, we investigated tissue and serum from glioma patients that revealed differences in the metabolome between glioblastoma and oligodendroglioma, as well as between oligodendroglioma grade II and grade III. In addition, we discovered metabolite patterns associated to survival in both glioblastoma and oligodendroglioma. In our final work, we identified metabolite pattern differences between cell lines from a subgroup of glioblastomas lacking argininosuccinate synthetase (ASS1) expression, (ASS1 negative glioblastomas), making them auxotrophic for arginine, a metabolite required for tumor growth and proliferation, as compared to glioblastomas with normal ASS1 expression (ASS1 positive). From the identified metabolite pattern differences we could verify the hypothesized alterations in the arginine biosynthetic pathway. We also identified additional interesting metabolites that may provide clues for future diagnostics and treatments. Finally, we were able to verify the specific treatment effect of ASS1 negative cells by means of arginine deprivation on a metabolic level.